The regulator herein disclosed has special utility as a controller for air pressure and pneumatic suspension devices, such as air spring and pneumatic-hydraulic shock absorbers for highway vehicles. Regulators for this purpose currently in commercial use lack such features as (1) mechanism for maintaining minimum pressures in these devices when the air source fails; (2) adjustable valve structure for preselecting different minimum fail-safe pressures; and (3) adjustable indicia structure for indicating a desired pressure to which the suspension system can be returned after temporary departure from corresponding operating conditions of the vehicle. In their normal use, such regulators are mounted on or adjacent to the dash of a vehicle or in other proximity to an operator station.